When Frankie sets down his pen in the interrogation room for the suspect to use, it is on the right side of the pad. After a quick back-and-forth shot of their faces, the camera returns to show the suspect pick up the pen from the left side of the pad.
Amyl Nitrate is referred to as "poppers", by both Rizzoli and Isles (at least she doesn't correct it) when in fact it's an additive for diesel fuel. Poppers are Amyl Nitrite, with an "i".
The confession on the book refers to a bombing in Dublin yet in the next scene they are dealing with the British police. If it was in Dublin they should have been talking to the Irish Gardai.
Maura looks at the victim's hands and promptly declares the the bruising indicates the fingers were broken individually at five minute intervals. Saying the fingers were broken individually makes logical sense, but the bruising would not tell you that. More importantly. It is absolutely impossible to say the fingers were broken at five minute intervals.